Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this disclosure and are not admitted to be prior art by inclusion in this section.
Typically, an image sensor includes an array of pixel elements fabricated as an integrated circuit (IC) on a semiconductor substrate, such as silicon wafer. Very-large-scale integration (VLSI) is the process of creating an IC by combining thousands of transistors and other circuit elements into a single chip or die. The wafer serves as the substrate for microelectronic devices (e.g., image sensors) built in and over the wafer and undergoes many microfabrication process steps such as doping or ion implantation, etching, deposition of various materials, and photolithographic patterning. After the wafer is processed, the individual microcircuits or dies are separated (e.g., using wafer dicing) and packaged. The semiconductor wafer can include a number of dies. For example, a 300 millimeter (mm) (130) wafer (100) (i.e., 11.811 inches [″] or approximately [˜] 12″) can include 148-20 mm (132) square dies (110), as shown in FIG. 1. Dies typically refer to ICs prior to being packaged and encased in a supporting case (e.g., plastic) that prevents physical damage and corrosion. Chips typically refer to ICs after being packaged (or assembled) that include electrical leads that allow the ICs to be coupled to other electronic components.
A conventional image sensor has a relatively small die size (e.g., less than [<] 5×5 centimeters [cm]) and includes a two dimensional (2D) array of sensor elements (or pixels) that perform a similar function. Very large area complementary metal-oxide-semiconductor (CMOS) image sensors (e.g., greater than or equal to [≥] 5×5 cm) can provide improved imaging performance over conventional image sensor for some scenarios, such as medical imaging (e.g., x-ray imaging), as well as in other high end imaging applications in astronomy, cinematography, and other scientific imaging. The very large area CMOS image sensors are at least an order of magnitude (10×) larger than devices for which conventional CMOS imager manufacturing processes have been developed. CMOS imager manufacturing processes often rely on know-how developed for silicon wafer based semiconductor chip manufacturing, where rectangular dies used in chips are conventionally in the 1 to 25 mm size range. Thus, very large area CMOS image sensors are well outside the chip size range conventionally used by the semiconductor manufacturing technology field. The technology (circuitry, devices, and methods) described herein provides improvements in very large area CMOS image sensor circuit designs as well as conventional image sensors.